The present invention relates to an air-conditioning control system for automotive vehicles, which comprises a compressor of variable capacity type in which in response to an electric signal from the outside, the suction pressure is set to a selected one of various different values, to thereby enable the capacity to be varied in accordance with the set suction pressure.
Conventionally, an air-conditioning control system for automotive vehicles has been proposed, e.g. by Japanese Provisional Patent Publication (Kokai) No. 57-165684, in which the temperature or refrigerant pressure of an evaporator is detected as a parameter representative of the cooling degree of the evaporator, and the suction pressure of a variable capacity compressor is set on the basis of a signal indicative of the detected value, thereby effecting capacity control of the compressor.
In the conventional air-conditioning control system described above, the capacity control is carried out in the following manner. That is, for the purpose of prevention of the evaporator from being frozen, the suction pressure is set to a relatively high value to bring the capacity of the compressor to a relatively low value, so as to prevent the temperature on the outlet side of the evaporator from being lowered to a value equal to or lower than the freezing limit value. Because of such arrangement, in cold weather, when the air-conditioning control system is brought to a control mode carrying out demisting to remove mist on the front window pane of the automotive vehicle, if an intake door of the system is in a position to recirculate the indoor air, the demisting performance is insufficient or the demisting control is impossible, because the variable capacity compressor is in a low capacity running state or in a halt state.